High-frequency utilization apparatus for ionized gas



April 24, 1962 R. R. WARNECKE ETAL 3,031,399

HIGH-FREQUENCY UTILIZATION APPARATUS FOR IONIZED GAS Filed Nov. 12. 1959 INVENTORS Rob er! R WA R/VECKE e/ fid ae malhe V/N ENT BY .4

ATTORNEYS 3,031,399 HIGH-FREQUENCY UTILIZATION APPARATUS FOR IONIZED GAS Robert R. Warnecke and Germaine Vincent, Paris,

France, assignors to Compagnie Generals dc Telegraphic sans Fil, Paris, France l i Filed Nov. 12, 1959, Ser. No. 852,268

Claims priority, application France Dec. 8, 1958 Claims. (Cl. 204-1932) The present invention relates to an apparatus in which a strongly ionized gaseous medium is confined within an evacuated vessel by means of a high-frequency electromagnetic field, and more particularly to an apparatus provided with one or several cavity resonators confining and compressing therein, by means of a high-frequency electromagnetic field, a strongly ionized gaseous medium so as to effectively insulate the same from the walls of the vessel to enable sufiicient heating of the resulting so-called plasma with a goal to produce a thermo-nuclear fusion reaction.

Devices are known in the prior art of nuclear physics which include a casing or vessel filled with a strongly ionized gas, that is, in the status of plasma, which is subjected to a confining action within a portion of this casing or vessel for the purpose of compressing the same within said portion, and, on the other hand, to thermally insulate or isolate the plasma from the walls of the casing or vessel with a view to obtain an eificient heating of the plasma that may eventually lead to nuclear fusion reactions.

However, in the prior art devices utilizing a cavity resonator, difiiculties arise in the operation thereof due to the fact that the resonant frequency of the cavity changes in the course of the formation of the plasma. As the resonant frequency of the cavity undergoes changes, the fixed frequency output from the oscillator producing the high-frequency electromagnetic field at a predetermined frequency no longer bears the desired relationship to the resonant frequency of the cavity, i.e., the frequency of the electromagnetic field set up within the cavity resonator no longer corresponds to the resonant frequency of the cavity. It follows therefrom that as soon as the high-frequency oscillator is not tuned to the resonant frequency of the cavity, the efiiciency of the system decreases by the reduction in the electromagnetic field within the resonator cavity which, in turn, decreases the compression effect on the plasma.

The present invention is concerned with a system improving the prior art devices and eliminating therefrom the shortcomings and disadvantages thereof mentioned hereinabove.

Accordingly, it is an object of the present invention to provide an apparatus for compressing a strongly ionized gaseous medium within a cavity resonator by means of an electromagnetic high-frequency field which eliminates and obviates the inconveniences and shortcomings of the prior art devices and which also assures a relatively high efi'iciency throughout the entire course of the operation of the device and of the formation of the plasma.

Another object of the present invention is the provision of an apparatus for confining and compressing a strongly ionized gas within an enclosure formed by a cavity resonator by means of an electromagnetic field which includes means to assure a continuous tracking of the output frequency of the electromagnetic-field-producing oscillator with the resonant frequency of the cavity Within which the gas is confined andcompressed.

Still another object of the present invention resides in the provision of automatic frequency control means for use with the source producing a high-frequency electromagnetic field in an apparatus of the type described hereinabove in which a strongly ionized gas is compressed nited tates atet within a confined resonant space by means of which the high-frequency electromagnetic field is tuned to the resonant frequency thereof so as to effectively confine and compress the gas.

These and other objects, features and advantages ofthe present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows in the single figure thereof, for purposes of illustration only, an automatic frequency control system for use with a prior art apparatus for confining and compressing a heavily ionized gaseous medium.

Referring now to the drawing which illustrates in the schematic diagram of the single FIGURE thereof the present invention in connection with a known prior art arrangement, reference numeral 1 designates therein a quartz tube in communication, by means of conduit 2, with the source 3 for the admission or input of the gas and with the pump 4. The ends of the tube 1 are open or suitably perforated, and penetrate, in a vacuum-tight manner, into the inside of cavity resonators 5 and 6. A high frequency electromagnetic field is excited within the cavity resonators 5 andf6 by means of the energy produced by the high frequency generator or oscillator 7 and propagated or transmitted through the conduits or Wave guides 8 and 9 to the resonator cavities 5 and 6.

The frequency of the generator 7 is usually tuned to coincide with the resonant frequencies of the cavities 5 and 6. The vessel or casing of the installation which is evacuated is defined or delimited by means of windows 10 and 11 through, which the'electromagnetic energy may flow. The assembly is also placed in an axial magnetic field produced by the windings or coils 12. The elements described so far hereinabove by reference to the single figure of the drawing are all of known conventional construction and may be realized in any manner known in the prior art.

The operation of the prior art devices described so far hereinabove is as follows:

After having admitted gaseous medium from the source 3 into the tube 1 and after having established a very low pressure by means of the vacuum pump 4, a high-frequency electromagnetic field is established within the cavities 5 and 6. This electromagnetic field which is relatively intense since the generator 7 is tuned to the resonant frequency of the cavities 5 and 6, thereby ionizes the gaseous medium present within the cavities 5 and 6 whereupon the tube 1 fills itself with plasma. The plasma is thereby confined to the vicinity of the axis of the tube 1 by the magnetic field produced by the coils 12. At the same time, as may be readily demonstrated theoretically as well as experimentally, the high-frequency field exercises on the plasma a pressure which displaces the plasma from the cavities 5 and 6 into the tube 1. The density of the plasma thereby increases within the tube -'1 and decreases correspondingly within the cavities 5 and 6-, the corresponding'values thereof being relate-d to each other. It also follows therefrom that the plasma is compressed within the space thermally insulated from the walls of the tube 1, a space in which the plasma is confined by the magnetic field.

However, experience also has clearly established that the operation of such a prior art device is disturbed by the variation in the resonant frequency of the cavities 5 and 6 which is caused as the plasma is formed. Consequently, the formation of the plasma entrains a detuning of the cavities 5 and 6 with respect to the normally fixed output frequency of the generator 7 resulting in a lowering or reduction of the high-frequency field, a fact which may be very important. Furthermore, the compression of the plasma is very inetficient as a result thereof;

The present invention aims at an improvement over such a prior art device by completely eliminating the disadvantages encountered in connection therewith.

According to the present invention, the variations in the density of the plasma within tube 1 which, as pointed out hereinabove, are related to the variations in the density of the plasma within the cavities 5 and 6, a density upon which also depends the resonant frequency of the cavities 5 and 6, are utilized to derive therefrom a signal applied to the high-frequency oscillation generator 7 which itself is of the type adapted to be electronically tuned in such a manner as to automatically re-tune the generator 7 to the resonant frequency of the cavities 5 and 6 by taking into consideration the presence of the plasma so that the detuning effect is effectively annulled and the high-frequency field within cavities 5 and 6, as well as the density of the plasma within tube 1, are retained at the maximum pos- Sible value thereof.

The present invention also aims at a practical realization with simple means to translate the variations in the density of the plasma into an electrical signal adapted to perform this control function.

The present invention will be better understood by reference again to the single FIGURE of the drawing, and,

, in particular, to the elements thereof designated by reference numerals 13 to 19 which embody the present invention as applied to the prior art device.

As mentioned hereinabove, the generator or oscillator 7 is assumed to be of the type adapted to be electronically tuned. Any suitable oscillator may be used for that purpose, though the present invention proposes in particular the use of a backward wave oscillator, known under the trade name of *Carcinotron, which offers the advantage to deliver an essentially constant power output over a relatively large tuning band. A second generator 13 of any suitable type and having a fixed frequency is also provided in accordance with the present invention, the output of which is transmitted through a wave guide 14 to a transmitter horn 15 which, in turn, transmits a Well-defined beam of high frequency energy across the plasma within the tube 1. A receiving horn 16 is disposed on the other side of the tube 1 which receives the electromagnetic wave energy after having been subjected to an attenuation and de-phasing in the course of its passage across the plasma within tube 1, this attenuation and dephasing being variable as a function of the density of the plasma. After detection of the received energy within a detector 17 which may be a simple rectifier or a phase-detector or discriminator circuit of any known type, as the case may be, a signal is obtained at the output thereof which varies with the density of the plasma. This output signal passes through a circuit 18 having a suitable transfer function or characteristic in order to adapt the law of the variations of the detected signal varying as a function of the density of the plasma within tube 1 to the law of frequency variation as a function of the control voltage of generator 7, and is thereupon applied by means of connection 19 to the input circuit of the control electrode of the generator or oscillator 7 in such a sense that the latter is re-tuned to the resonant frequency of the cavities 5 and 6 under the conditions of the presence within the tube 1 of plasma having maximum obtainable density when this tuning is realized.

The present invention results in a considerable improvement in the performance of the prior art device of the type described herein.

However, it is understood that the present invention is not limited to the details shown and described herein but is susceptible of many changes and modifications within the scope and spirit of the present invention. As mentioned hereinabove, any suitable known circuits or devices may be used to achieve the desired result in connection with elements 13 to 19. Additionally, the described means translating the variations in the density of the plasma as evidenced by the attenuation and/or de-phasing of the electromagnetic wave energy into an electric signal usable as automatic frequency control are not limited to the particular details described herein but may be replaced by other means known to a person skilled in the art.

Thus, it is quite obvious that the present invention is not limited to the details shown and described herein but may be varied and modified considerably within the spirit and scope of the present invention, and we, therefore, do not wish to be limited to the details illustrated herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. In an apparatus for compressing plasma, an evacuated vessel, means for admitting low pressure gas into said vessel, at least one cavity resonator having its interior in communication with said vessel, means for supplying highfrequency energy to said resonator to excite the same substantially at its natural resonance frequency thereby ionizing said gas to form plasma and pushing a part of said plasma away from said resonator into said vessel, means for confining said plasma within the interior region of said vessel, and means responsive to the plasma density in said vessel for automatically retuning said high-frequency supplying means to the natural resonance frequency of said resonator with plasma contained therein.

2. A combination as claimed in claim 1, wherein said high-frequency supplying means is a backward wave oscillator.

3. A combination as claimed in claim 1, wherein said returning means includes a beam source of microwave energy, means for directing said microwave energy beam through said plasma within said vessel, means for collecting said microwave energy after traversing said plasma, whereby at least one of the variables consisting of amplitude and phase of said microwave energy exhibits a magnitude depending on said plasma density, means for detecting at least one of said variables consisting of amplitude and phase to thereby obtain an electrical signal responsive to said plasma density, and means for applying said signal to said cavity resonator highfrequency supplying means to retune the same to a frequency corresponding to a plasma density maximum.

4. A combination as claimed in claim 1, wherein said high-frequency supplying means is a backward wave oscillator, and wherein said returning means includes a beam source of microwave energy, means for directing said microwave energy beam through said plasma within said vessel, means for collecting said energy after traversing said plasma, whereby at least one of the variables thereof consisting of amplitude and phase of said microwave energy has a magnitude depending on said plasma density, means for detecting at least one of said variables consisting of amplitude and phase in said energy to thereby obtain an electrical signal responsive to said plasma density, and means for applying said signal to said backward wave oscillator to electronically retune it to a frequency corresponding to a plasma density maximum.

5. In an apparatus for compressing an ionized gaseous medium, comprising an evacuated vessel including cavity resonator means, means for establishing a predetermined pressure within said vessel and for regulatnig the presence of said gaseous medium Within said vessel, means for supplying to said cavity resonator means high-frequency electromagnetic energy at the resonant frequency of said cavity resonator means to thereby enable the production of plasma from said ionized gaseous medium within said vessel, and means operatively connected with said high-frequency energy supplying means for automatically adjusting the output frequency thereof in dependence on the density of the plasma within said vessel to provide continuous correspondence between said resonant frequency and said output frequency.

6. In an apparatus for compressing a strongly ionized gaseous medium, comprising an evacuated casing including cavity resonator means, means for regulating the pressure and presence of said gaseous medium within said casing, means for supplying to said cavity resonator means high-frequency electromagnetic wave energy at the resonant frequency of said cavity resonator means to thereby ionize said gaseous medium and enable the formation of a plasma within a predetermined portion of said casing, and means operatively connected with said high-frequency energy supplying means for automatically adjusting the output frequency thereof in dependence on the density of the plasma to provide tracking between changes in said resonant frequency and the output frequency of said highfrequency energy supplying means.

7. In an apparatus according to claim 6, wherein said last-mentioned means includes means for directing electromagnetic wave energy through a portion of said plasma to thereby vary the characteristics of the electromagnetic wave energy as a function of the density of said plasma, means for receiving the electromagnetic energy after passage through said plasma portion and for detecting the changes in said characteristics to thereby produce a control signal, and means for applying said control signal to said high-frequency energy supplying means to thereby retune the same to the resonant frequency of said cavity resonator means.

8. In an apparatus according to claim 5, wherein said high-frequency energy supplying means includes a back- Ward wave oscillator adapted to be electronically tuned over a wide band.

9. In an apparatus for compressing strongly ionized gas, comprising an evacuated casing including cavity resonator means and space means for the formation of a plasma from said ionized gas, means for regulating the pressure and presence of said gas within said casing, means for supplying to said cavity resonator means high-frequency electromagnetic energy "at the resonant frequency thereof to thereby ionize said gas therewithin and enable production of plasma therefrom, means for confining said plasma Within said space means, and means operatively connected with said high-frequency energy supplying means for automatically adjusting the output frequency thereof in dependence on the density of the plasma within said portion to provide correspondence between said resonant frequency and said output frequency.

10. A method for continuously obtaining maximum plasma conditions in an evacuated casing having a cavity resonator which is supplied with high-frequency electromagnetic energy from a high-frequency energy generating device the output frequency of which essentially coincides with the resonant frequency of the cavity resonator, comprising the steps of transmitting a signal of high-frequency energy through the plasma to detect changes in the density thereof reflecting changes in the resonant frequency of the cavity resonator, and adjusting the output frequency of the high-frequency generating device as indicated by the changes in said signal to retune the generating device to the frequency of said cavity resonator.

References Cited in the file of this patent Australian J. of Physics, vol. 10, No. 1, March 1957, pp. 221-225 (an article by Knox), 204-1545.

Proceedings of the Second United Nations International Conference on the Peaceful Uses of Atomic Energy. Held in Geneva, September 1-13, 1958. Vol 32, United Nations, Geneva, 1958. An article by Vendeneove et al., pp. 239-244. 

1. IN AN APPARATUS FOR COMPRESSING PLASMA, AN EVACUATED VESSEL, MEANS FOR ADMITTING LOW PRESSURE GAS INTO SAID VESSEL, AT LEAST ONE CAVITY RESONATOR HAVING ITS INTERIOR IN COMMUNICATION WITH SAID VESSEL, MEANS FOR SUPPLYING HIGHFREQUENCY ENERGY TO SAID RESONATOR TO EXCITE THE SAME SUBSTANTIALLY AT ITS NATURAL RESONANCE FREQUENCY THEREBY LONIZING SAID GAS TO FORM PLASMA AND PUSHING A PART OF SAID PLASMA AWAY FROM SAID RESONATOR INTO SAID VESSEL, MEANS FOR CONFINING SAID PLASMA WITHIN THE INTERIOR REGION OF SAID VESSEL, AND MEANS RESPONSIVE TO THE PLASMA DENSITY IN SAID VESSEL FOR AUTOMATICALLY RETUNING SAID HIGH-FREQUENCY SUPPLYING MEANS TO THE NATURAL RESONANCE FREQUENCY OF SAID RESONATOR WITH PLASMA CONTAINED THEREIN. 